Intermittently-lapped extendible boom



April 13, 1965 sw 3,177,987

INTERMIT'IENTLY-LAPPED EXTENDIBLE BOOM Filed FGb. 26, 1962 FRANK H.SWAIM INVENTOR BY w ATTORNEYS United States Patent 3,177,987lNTERMITIENTLY-LAPPED EXTENDIBLE BOOM Frank H. Swaim, Silver Spring, Md,assignor to the United States of America as represented by the Secretmyof the Navy Filed Feb. 26, 1962, Ser. No. 375,855 4 Claims. (Cl. 18934)This invention relates generally to extendible booms of the typeutilized for radio antennas and the like; more specifically, it relatesto an improved extendible boom construction that is more rigid andlighter in weight than present extendible booms.

Extendible booms of the type to which this invention relates areutilized where an antenna-like structure is re quired that can beinitially carried in a compact, collapsed condition and which may beerected into a rod or boom several feet in length when required. Onepresent collapsible and extendible boom of this variety is that shown inUS. Patent 2,157,278, to R. B. Blackmore, the boom or antenna of thisdevice consisting of a narrow fiat tape several feet in length whichpossesses the characteristic that when it is not constrained in its flatcondition it will form into a tube. The flat tape is initially woundupon a drum or spool, much in the manner of a carpenters conventionalcollapsible steep rule. When it is desired to erect the boom the tape ismerely unwound from the spool. The free end of the tape passes throughan encirciing mandrel which tends to guide it smoothly into itsnaturally tubular shape, and the result is a tubular boom several feetin length.

The Blackmore extendible boom has the advantages that the spool erectingunit is quite compact, and that the boom itself, being constructed offairly thin metal, is relatively light in weight. Hence, the completeunit is quite adaptable to the limited space and weight requirements ofaircraft, missiles and space satellites. The Blackmore boom is, however,not as rigid as is desired for some applications, especially where it isto be utilized in a satellite to support a weight mass.

It has been found that the attitude relative to the earth of a spacesatellite may be controlled by the method referred to as gravityorientation. In this method a weight mass is positioned at a distance ofseveral feet from an orbiting satellite, the two being connected by aboom. The satellite will then so align itself that the centers ofgravity of the satellite, the mass weight, and the earth lie on astraight line, a position that is maintained as the satellite circlesthe earth. The boom utilized in this method must be collapsible withinthe satellite during launching thereof, and must then be easilyextendible when the satellite has entered its orbit. Additionally, theboom must be somewhat rigid when erected, for even though a condition ofweightlessness exists in space there are still other forces to contendwith. Finally, the boom and its erecting apparatus must be as light inweight as possible.

When a boom similar to that shown in the patent is employed in asatellite gravity orientation system it has been found that the edges ofthe tape must be overlapped for an arc length which often exceeds 180degrees, which overlapping requires extra width for the tape and henceadditional weight. Moreover, the added tape width requires a largerstorage spool and larger erecting apparatus. It is highly desirable,especially because of the limited space and weight allowances in spacevehicles, to provide a boom which is as light in Weight and as small insize as is possible for a given desired rigidity. The improved boom ofthe present invention satisfies these requirements.

3,177,98? Patented Apr. 13, 1965 ice It is an object of this invention,therefore, to provide an improved extendible boom so constructed that itmay be readily erected and collapsed, and which when erect issubstantially rigid and capable of withstanding considerable torsionaland deflective loading.

A further object of this invention is to provide an extendible boom thatis lighter in weight and that occupies less volume than previous boomsof the same general type.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings, wherein:

FIG. 1 is a perspective of the extendible boom of the invention, showingthe manner in which it assumes a tubular shape as it is unrolled from astorage spool;

- FIG. 2 is an elevation view showing a portion of the boom with thenotches and tabs along the mating edges thereof in confronting,unengaged position; and

FIG. 3 is a view in elevation showing the manner in which the tabs andnotches engage to provide a substantially rigid boom.

In the extendible boom of the invention a narrow, elongated strip ofthin, resilient metal is first so formed that in its normal unrestrainedcondition it will form itself into the opposite edge thereof. When theboom has assumed its tubular shape with the notches and tabs interlockedit becomes quite rigid, the natural resiliency of the strip serving tokeep it in its tubular shape. When it is desired to collapse the boom itis merely rolled upon a storage spool much in the same manner as acarpenters flexible steel measuring rule. The boom of the invention isuti lized with known erecting apparatus, such as is shown in said Patent2,157,278, which apparatus includes an encircling cylindrical die tofacilitate the strips transition from a fiat to a tubular state andreturn. Since the erecting apparatus is not a part of the invention itwill not be described herein.

Referring now to the drawings, the extendible boom of the invention isshown in perspective in FIG. 1, and consists of a narrow, several feetin length, strip 10 of very thin material. The strip is constructed ofberyllium copper or a similar material, and is but a few thousandths ofan inch in thickness (the thickness of the strip is exaggerated in thedrawings for clarity). The upper and lower edges 12 and 14 thereof eachhave a plurality of notches 16 and tabs 18 thereon, the notches on oneedge being directly opposite the tabs on the opposite edge. As is bestshown in FIG. 2, the sides of the notches 16 are defined by the sideedges 20 of the tabs, which edges are slightly tapered so that thenotches flare outwardly.

The strip 10 is fabricated in a manner whereby it naturally tends toform into a tubular shape. The strip is made from a flat piece ofmaterial, the notches and tabs first being formed therein. Then thestrip is wound into an elongated tube, with the edges 12 and 14overlapping for about degrees arc length. The tube is then subjected toa heat treating process which causes it to assume a permanent set and tobecome resilient. Thereafter the strip is made fiat and is wound upon astorage spool 22. It is emphasized that during the forming stage theedges 12 and 14 are overlapped for a substantial arc length, and thatthe notches and tabs are not interlocked during this time. Theoverlapping arc length during heat treating is substantially greaterthan the overlapping arc length of the edges 12 and 14 when the tabs andnotches are interleaved.

When it is desired to form the extendible boom the strip is unwrappedfrom its spool, and over a transition distance A the opposite edges 12and 14 move toward each other until the tabs 18 on each edge are alignedwith notches 16011 the opposite edge (FIG. 2). Movement of the edgescontinues until the tabs and notches interleave (FIG. 3) the taperededges 20 facilitating this occurrence. The tubular boom is thus formed.

Because the circumference of the tube when the tabs and notches areinterlocked is substantially greater than was the circumference thereofduring the time when it was being heat treated, and because the inherentresiliency of the tube tends to make it circumferentially compressitself toward the permanent set position it acquired during heattreatment, the tabs and notches will tend to stay interlocked under mostcircumstances. The resultant extendible boom is capable of withstandingconsiderable bending and twisting without collapsing, and is farstronger in this regard than the merely overlapped construction ofprevious similar booms. Moreover, because the strip has cut-out portionsand is substantially smaller in width for the same boom diameter thanbooms wherein extensive overlapping is required it is somewhat lighterin weight than such overlapped booms. The reduction in strip width alsoreduces the size of the storage spooland of other components of theerecting unit, thus resulting in a further weight reduction. Naturally,the smaller size apparatus resulting from the invention also requiresless space wherever it is utilized.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. An extendible element, comprising an elongated, narrow strip havingalternating notches and tabs formed on the opposite longitudinal edgesthereof, the tabs on one edge being positioned opposite the notches onthe other edge, said strip being resilient and being so fabricated thatit tends to form into an elongated tube the longitudinal axis of whichlies parallel to the longitudinal center line of said strip.

2. An extendible element as claimed in claim 1, wherein said notches aredefined by said tabs, and wherein said tabs are progressively narrower,moving from the central portion of said element transversely toward theextreme longitudinal edges thereof.

3. In an extendible antenna device, an extendible element comprising anelongated, relatively thin, narrow strip having alternating tabs andnotches formed on the opposite longitudinal edges thereof, said notchesbeing defined by said tabs and the tabs on one edge being positionedopposite the notches on the other edge, said strip being resilient andhaving a predetermined set so that when unrestrained it tends to forminto an elongated tube the longitudinal axis of which lies parallel tothe longitudinal center line of said strip, said predetermined set insaid resilient strip being such that the strip tends to form a tubehaving a circumference substantially'less than the arc length measuredbetween the bottom edge of oppositely positioned tabs on the edges ofsaid strip, whereby said tabs and notches are resiliently urged intointerlocking engagement when said strip assumes a tubular configuration.

4. An extendible element as claimed in claim 3, wherein said tabs areprogressively narrower, moving from the central portion of said stripelement transversely toward the extreme longitudinal edges thereof, andwherein said strip element measures a few thousandths of an inch inthickness.

References Cited by the Examiner UNITED STATES PATENTS 2,130,993 9/38Dubilier 189-23 2,903,282 9/59 Miller -15 3,144,104 8/64- Weier et a].189-34 RICHARD w. COOKE, JR., Primary Examiner. JACOB L. NACKENOFF,Examiner.

3. IN AN EXTENDIBLE ANTENNA DEVICE, AN EXTENDIBLE ELEMENT COMPRISING ANELONGATED, RELATIVELY THIN, NARROW STRIP HAVING ALTERNATING TABS ANDNOTCHES FORMED ON THE OPPOSITE LONGITUDINAL EDGES THEREOF, SAID NOTCHESBEING DEFINED BY SAID TABS AND THE TABS ON ONE EDGE BEING POSITIONEDOPPOSITE THE NOTCHES ON THE OTHER EDGE, SAID STRIP BEING RESILIENT ANDHAVING A PREDETERMINED SET SO THAT WHEN UNRESTRAINED IT TENDS TO FORMINTO AN ELONGATED TUBE LONGITUDINAL AXIS OF WHICH LIES PARALLEL TO THELONGITUDINAL CENTER LINE OF SAID STRIP, SAID PREDETERMINED SET IN SAIDRESILIENT STRIP BEING SUCH THAT THE STRIP TENDS TO FORM A TUBE HAVING ACIRCUMFERENCE SUBSTANTIALLY LESS THAN THE ARC LENGTH MEASURED BETWEENTHE BOTTOM EDGE OF OPPOSITELY POSITIONED TABS ON THE EDGES OF SAIDSTRIP, WHEREBY SAID TABS AND NOTCHES ARE RESILIENTLY URGED INTOINTERLOCKING ENGAGEMENT WHEN SAID STRIP ASSUMES A TUBULAR CONFIGURATION.